Superficial Layers Flashcards
Explain the major difference between gram negative and gram positive Bacteria
Gram negative bacteria - They have two membranes separated by a THIN peptidoglycan layer.
Outer membrane : Periplasm + peptidoglycan : cytoplasmic membrane
Gram positive bacteria - Do not have an outer membrane. They have a THICK peptidoglycan outer layer and then the PM. Periplasm is in between them
What is the S layer ?
- found in most archaea and a lot of bacteria
- A 2D lattice structure that covers the entire cell with identical protein sub units
- typically these are glycoproteins
- it is expensive to make for the cell
Why is the S layer often lost in the lab?
By chance during the transfer of cells a mutant has arisen that cannot develop the S layer. However in pure culture mutants that cannot produce it have a growth advantage because the Lab cell does not need protection from viruses and pathogens
how is the S layer built?
it is built via a self assembly system. It does not have any covalent interactions with the cell wall. Only ionic and hydrophobic. Each subunit also interacts with eachother through non covalent forces.
What type of forces hold the S layer to the cell wall and the s layer subunits together?
Anything but covalent bonds!!!
Ionic, hydrophobic, and hydrogen bonds mainly
What are the three types of S layers known?
1) hexagonal with P6 symmetry
2) Tetragonal with P4 symmetry
3) linear with P2 symmetry
What S layers are rare, what are most common to archaea?
P6 is the most common Archaea S layer
P2 is rare
Explain the characteristics of S layer proteins
- usually acidic
- Usually large proteins
- contain amino acids that lack Sulphur
- THE SPACING OF PROTEINS IS CONSTANT THROUGHOUT THE LAYER THIS DEFINES PORE SIZE
- called center to center spacing
True or false, organisms always make an S layer of the same symmetry
True
What are usually the most abundant proteins in an archaea or bacteria cell?
S layer proteins
What agents would you use to isolate the S layer proteins?
urea or guanidine HCl
any detergents
chelating agents (EDTA)
Explain S layer synthesis in terms of genes and copies of proteins
The entire S layer is produced from a single gene
therefore it needs a strong promoter
10% of proteins in the bacterium
If a bacteria has a doubling time of 20 minutes it needs to be able to produce 500 proteins / second for the S layer. This explains why Lab cells lose their S layer.
Explain the main function of the S layer
- protection from viruses and predatory prokaryotes
- acidity may aid in an ion trap
- in some archaea it defines the shape
- adhesion
when does the S layer directly interact with the plasma membrane?
Never in bacteria. Only in
Archaea
What is Treponema?
A bacterium with an S layer . This causes syphilis
How are S layers used in commercial use?
Because S layers have centre to centre spacing that creates a defined pore size, they make good filters
they have more uniform size than polymer base systems (they can filter things that polymer filters cannot)
What is an extracellular polysaccharide? EPS
- like the S layer it is a complex on the surface of the cell
- unlike the S layer, it can extend up to 50um from the cell
- Most common EPS’s are slime, capsule, and glycocalyx
- for us thought we refer to it all as capsule
Why is EPS lost in the lab usually?
EPS’s are very expensive to make so mutants in lab without it have growth advantage
What is the composition of most extracellular polysaccharides?
they are very hydrated, up to 98% water
They are also acidic much like S layer proteins.
It is visible under a light microscope!
Why is it difficult to treat cystic fibrosis? What bacteria causes this?
- pseudomonas aeruginosa produces a shit load of capsule that blocks any drugs from acting against its pathogenic properties. The capsule stops drug effectiveness
What is the composition of EPS?
Polysaccharides
there is one exception for EPS that does not contain monosaccharides
that is a proteinaceous EPS called polyglutamate
explain homopolymers vs. heteropolymers
Homopolymers are composed of a single type of monomer: cellulose or dextran
heteropolymers: mixed monomers
What is the major function of having an EPS
- protects cells from extreme dryness called desiccation
- protects cells from predators
- stop a phagocyte from eating the cell
- evasion of immune response: many pathogens have it for this reason.
- adherence in biofilms
Why are biofilms a problem in medicine and economics? what commercial use is capsule used for?
many pathogens create extensive capsule which causes problems with medical catheters and industrial pipelines
capsule is used as a thickening agent in food
